The present invention relates to the manufacture of reinforced polymeric articles and, in particular, to continuously molded composites comprising a polyurethane core and polyurethane skin structurally integrated at a three dimensional high modulus interface.
Foamed polyurethane products having integral reinforcements for imparting increased strength to a core have been formed in both batch and continuous processes. For example, in U.S. Pat. Nos. 4,163,824 and 4,073,840, there is disclosed a method and apparatus for producing fiber-reinforced foam articles wherein randomly oriented fiber filaments are dispersed throughout a core. This produces a foamed product of substantially uniform density. Another batch process is disclosed in U.S. Pat. No. 4,130,614 wherein woven glass mats reinforce the top and bottom surfaces of a foamed article with the glass mats captured entirely within a higher density outer foam layer which surrounds a lower density inner core. The major surfaces may include a film layer adhered to the outer foam layer. A similar material is also disclosed in U.S. Pat. No. 3,895,159 wherein a glass fabric is embedded in at least one noncellular surface layer.
Continuous processes have been disclosed for the manufacture of foamed articles, particularly laminated foams. For instance, U.S. Pat. Nos. 3,686,047; 4,496,625; 4,555,442; Re. 30,984; 3,142,864; and 3,903,346, disclose continuous foam laminates wherein structural facing sheets of materials such as foils, films, and the like are laminated to the inner foam core during an open-ended forming process.
In the above approaches to reinforcing the foam, certain physical characteristics are improved while others are not. The laminates improve flexure strength and to an extent longitudinal compressive strength in comparison with the foam core alone. However, only an adhesive bond and not a mechanical bond is effected between the foam and the laminate. Accordingly, this presents a relatively weak shear interface, particularly under high cyclical loadings. Such articles are prone to fracturing at the interface with a resultant loss of product intergity.
It would be desireable to provide, in view of the foregoing limitations, a reinforced polymeric composite system with improved static and dynamic characteristics as a load bearing member which system provides increased design flexibility within existing thermoset chemistry and can be accurately produced in a continuous process.